Substituted 2,3-dihydro-,4-oxathiin plant growth stunting agents

ABSTRACT

Substituted 2,3-dihydro-1,4-oxathiins of the formula ##SPC1## 
     Display useful plant growth regulant effects including herbicidal effects. Examples are 2,3-dihydro-5,6-diphenyl-1,4-oxathiin, and 2,3-dihydro-5-(4-methyl-phenyl)-6-phenyl-1,4-oxathiin 4-oxide. The compounds are useful for the selective control of grasses and as dwarfing agents, as well as for inhibition of vegetative and reproductive axillary growth, and for increasing the sugar content of sugar producing species. A number of these are new compounds. 
     This invention relates to a method of regulating the growth of plants and to plant growth regulant compositions useful in such method, as well as to chemical compounds useful in such compositions. 
     Regulation of the growth of plants is frequently desirable for a number of reasons. For example, the control of weeds is of great economic importance. Weed competition inhibits the production of foliage, fruit or seed of agricultural crops. The presence of weeds may also reduce the quality of the harvested crop and reduce harvesting efficiency. Weed control is essential for maximum production of many agronomic and horticultural crops, including corn (Zea mays L.), rice (Oryza sativa L.) and soybeans (Glycine max (L.) Merr.). Weeds on non-cropped areas may cause a fire hazard, undesirable drifting of sand or snow, impaired beauty of the landscape and irritation to persons with allergies. The invention, in one aspect, is based on the discovery that certain substituted 2,3-dihydro-1,4-oxathiins are remarkably effective preemergence herbicides, especially for the selective control of grasses. 
     Another form of regulation of plant growth that is of great economic importance involves non-herbicidal growth regulant effects. These include, by way of nonlimiting example, such effects as dwarfing, antitranspiration, inhibition of vegetative and reproductive axillary growth and increasing the sugar content of sugar producing species. In one important aspect the invention provides a highly effective method for producing such effects, employing certain substituted 2,3-dihydro-1,4-oxathiins. 
     The substituted 2,3-dihydro-1,4-oxathiins employed to produce herbicidal and other plant growth regulating effects in accordance with the invention are those of the formula ##SPC2## 
     Wherein the R&#39;s are the same or different and are selected from the group consisting of hydrogen, lower alkyl (especially methyl and ethyl), halogen (e.g., chlorine, bromine, fluorine), lower alkoxy (e.g., methoxy), amino, lower alkylthio (e.g., methylthio), and lower acyloxy (e.g., acetyloxy), and n is zero, 1 or 2. The compound wherein all of the R&#39;s are hydrogen, and n is zero, namely, 2,3-dihydro-5,6-diphenyl-1,4-oxathiin, is known [Marshall and Stevenson, J. Chem. Soc. 2360 (1959)]; the other compounds are believed to be new. 
     In a preferred class of compounds useful in the invention the R&#39;s have the following values: 
     R 1  = H 
     R 2  = H, CH 3 , C 2  H 5   
     R 3  = H, Cl, CH 3   
     R 4  = H, Cl, CH 3  ##EQU1## 
     R 6  = H, Cl, CH 3   
     R 7  = H, Cl, CH 3 , OCH 3   
     R 8  = H, Cl, Br, F, CH 3 , C 2  H 5 , OCH 3 , NH 2   
     R 9  = H, CH 3   
     R 10  = H. 
     Again, the members of this preferred class of compounds are new, except where all of the R&#39;s are hydrogen and n is zero (i.e., except for 2,3-dihydro-5,6-diphenyl-1,4-oxathiin). 
     Of special interest are the compounds of the class described having substituents on one or both phenyls, or a substitutent on the dihydro portion of the 1,4-oxathiin ring, or a combination of both. Also of special note are such compounds with a para substituent on the 5-phenyl group. 
     In one respect, the invention is concerned with chemicals of the kind described wherein n is 1 or 2, and use thereof in plant growth regulation. 
     In another respect the invention is directed to chemicals of the above-stated formula in which at least one of the R&#39;s is other than hydrogen or lower alkyl, as well as plant growth regulant uses of such chemicals. 
     The substituted 2,3-dihydro-1,4-oxathiins employed in the invention may be prepared by reacting a 2-mercaptoalkanol with an appropriately substituted 2-halo-2-phenylacetophenone in the presence of a base and cyclizing the resulting intermediate with water removal in the presence of p-toluenesulfonic acid as a catalyst. The preparation of the 2-halo-2-phenylacetophenones may be achieved using one of the following general procedures: 
     a. Reaction of a substituted benzoin with thionyl chloride. 
     b. Reaction of a substituted 2-phenylacetophenone with sulfuryl chloride. 
     c. Reaction of a substituted 2-phenylacetophenone with bromine. The 2-phenylacetophenones may be prepared by the standard methods known in the literature, such as Friedel-Crafts acylation or Grignard condensation with the appropriate chemicals. 
     The 2,3-dihydro-1,4-oxathiin in which n is zero may be oxidized to the corresponding 4-oxide or 4,4-dioxide (n = 1 or 2) by controlled addition of one or two equivalants respectively of a 30% hydrogen peroxide solution to one equivalent of the oxathiin in glacial acetic acid. 
     In one aspect, the invention contemplates application of any of the substituted 2,3-dihydro-1,4-oxathiin compounds described, in amount effective to regulate growth, to a locus at which such growth regulant effects as preemergence herbicidal effects, dwarfing, fruiting body inhibition, increasing sugar content, etc., are desired. In another aspect, the invention is directed to a plant growth regulant composition comprising a chemical compound as described herein, in amount effective to regulate the growth of plants, in admixture with a carrier therefor. It will be understood that the term plants as used herein includes plant parts such as foliage, roots, flowers and seeds. 
     The amount of substituted 1,4-oxathiin employed follows conventional practice for herbicidal use or other plant growth regulant uses and the chemical is suitably applied as a formulation in accordance with conventional agricultural chemical practice. 
     Thus, the chemical may be impregnated on finely-divided or granular inorganic or organic carriers such as attapulgite clay, sand, vermiculite, corn cobs, activated carbon or other granular carriers known to the art. The impregnated granules may then be spread on the soil. Furthermore, the chemical may be formulated, for example, as a wettable powder by grinding it into a fine powder and mixing it with an inactive powdered carrier to which a surface active dispersing agent has been added. Typical powdered solid carriers are the various mineral silicates, e.g., mica, talc, pyrophyllite, and clays. The wettable powder may then be dispersed in water and sprayed on the soil surface, or on crop plants. Similarly, an emulsifiable concentrate may be prepared by dissolving the chemical in a solvent such as benzene, toluene, or other aliphatic or aromatic hydrocarbon to which a surface active dispersing agent has been added. The emulsifiable concentrate may then be dispersed in water and applied by spraying. Suitable surface active agents are well known to those skilled in the art, and reference may be had to McCutcheon&#39;s Detergents and Emulsifiers, 1970, Allured Publishing Corp., Ridgewood, N.J., or Hoffman et al. U.S. Pat. Nos. 2,614,916, cols. 2 to 4 and 2,547,724, cols. 3 and 4, for examples of appropriate surface active agents. The concentration of active chemical in the formulation may vary widely, e.g., from 1 to 95%. The concentration of active chemical in dispersions applied to the soil or foliage is almost invariably from 0.002% to 75%. The chemical is frequently applied at rates of 0.10 to 25 pounds per acre. For use as a preemergence herbicide, the chemical is applied to soil which contains weed and crop seed (either to the surface of the soil or incorporated into the upper one to three inches of soil). The chemicals may be employed individually, or as a mixture of two or more chemicals. 
     The most suitable rate of application in any given case will depend on such factors as the particular response desired, soil type, soil pH, soil organic matter content, wind velocity, the quantity and intensity of rainfall before and after treatment, the air and soil temperature, light intensity and light duration per day. All of these factors can have an influence on the efficacy of the chemicals for a given plant growth control use. 
     The herbicidal use may include selective weed control in crops such as soybeans, sugar beets, etc. 
     Depending on crop, variety, dosage, time of application and certain cultural practices, growth regulating effects which are obtained include the following: 
     a. dwarfing 
     b. cessation of terminal growth 
     c. inhibition of axillary and intercalary growth 
     d. flowering inhibition 
     e. fruiting body inhibition 
     f. twisting and epinastic responses 
     g. modification of root growth 
     h. increasing sugar in sugar producing species 
     i. antitranspiration to control water loss. 
     The foregoing responses are general plant responses any one of which could contribute directly to yield increases. For example, a spray application may be made to tobacco after the flowers are removed to obtain excellent axillary growth control. It may be applied to cotton to facilitate a cut off spray or it may be applied on cotton early to retard the development of rank cotton. Chemicals described herein also may be used on ornamental plants. For example, a spray application may be made to chrysanthemums to obtain disbudding which, if done by hand, is very costly. It has been shown to increase the percent sugar in sugarcane. It can be postulated from the results on sugarcane that the chemicals may be preventing breakdown of sugars. The chemicals have also shown remarkable properties in inhibiting flower bud development on peaches. This is useful for preventing frost damage in marginal growth areas where late frosts are inevitable. Flower thinning may be accomplished also. 
     Another plant growth regulant effect that the chemicals of the invention exhibit is that of antitranspiration. The chemicals control stomatal opening and hence prevent excessive water loss. Due to this response greater yields can be obtained with plants growing under stress. 
     The following examples, in which all quantities are expressed by weight unless otherwise indicated, will serve to illustrate the practice of the invention in more detail. Examples 1-51 involve preparation of typical plant growth regulant chemicals of the invention, employing four different methods of preparation, identified by the letters A to D in TABLE I, as follows: 
     A. Halogenation of the appropriate 2-phenylacetophenone followed by reaction with a 2-mercaptoalkanol and cyclization. 
     B. Reaction of a purified 2-halo-2-phenylacetophenone with a 2-mercaptoalkanol followed by cyclization. 
     C. Oxidation of the appropriate 1,4-oxathiin with one equivalent of oxidizing agent. 
     D. Oxidation of the appropriate 1,4-oxathiin with two equivalents of oxidizing agent. 
     The identity of each of the compounds in the working examples was established partly by nuclear magnetic resonance spectrum and partly by analytical data. The n.m.r. spectra of the compounds revealed the characteristic couplings due to the protons of the dihydro portion of the dihydro-1,4-oxathiin ring, thereby confirming the structure. 
     In Examples 52-60 and TABLES II-IX the various substituted 1,4-oxathiins are identified by the Example numbers given in TABLE I. 
     Preferred new chemicals of the invention are those selected from the group consisting of the chemicals of Examples 3, 4, 2, 20, 21, 22, 9, 10, 6, 12 and 16; especially preferred are the chemicals of Examples 3, 20 and 21. 
     Plant growth regulant compositions of particular interest containing the present chemicals are those based on chemicals selected from the group consisting of 1, 3, 9, 12, 20, 21, 16, 17, 18, 29, 30 and 38, more preferably those based on chemicals 1, 3, 20, 21 and 12. 
     For use in preemergence control of weeds the preferred chemicals are those of Examples 3, 20, 21, 30, 38, 10, 16, 18, 13, 24 and 43, more especially the chemicals of Examples 3, 21, 18, 10 and 13. 
     Preferred plant growth retardant chemicals are those of Examples 1, 20, 29, 30, 38 and 9, more preferably Examples 1 and 20. 
     For inhibition of axillary vegetative and reproductive growth, preferred chemicals are those of Examples 1, 3, 9, 12, 20, 21, 16, 17 and 18, more preferably 1, 3, 20, 21 and 12.

EXAMPLE I Preparation of 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin from 2-Phenylacetophenone and 2-Mercaptoethanol. (Method A)

Powdered 2-phenylacetophenone (1021 g., mp. 55°-57°) was charged into a three-necked flask equipped with a strong mechanical stirrer, a reflux condenser and a dropping funnel. Sulfuryl chloride (430 ml.) was added in a continuous stream, over 10 minutes, with vigorous stirring. The reaction mixture was kept molten by heating on a steam bath for 1/2 hour. Benzene (2.5 l.) was added to the reaction mixture and a portion (300 ml.) of the solvent was removed under reduced pressure to remove excess sulfuryl chloride. The reactor was cooled to 20° in an ice bath and a stream of ammonia was bubbled into the solution. After 15 minutes, 2-mercaptoethanol (385 ml.) was added during 1/2 hour (the reaction mixture temperature remained below 50°). The ammonia sparge was continued for four additional hours and the reaction mixture was left at room temperature overnight. A cold solution of hydrochloric acid (1500 ml.). prepared by pouring 37% acid (600 ml.) over crushed ice (900 ml.), was poured into the reactor with stirring. After 15 minutes, stirring was stopped and the reaction mixture separated into two layers. The benzene layer was separated, p-toluenesulfonic acid (20 g.) was added and the reaction mixture was heated under reflux for 4 hours with azeotropic water removal. After cooling, the benzene solution was successively washed with 1.0 N sodium hydroxide solution (1000 ml.), water (500 ml.), filtered, and evaporated under reduced pressure. The warm syrup was then poured slowly into isopropyl alcohol (2.5 l.) with vigorous stirring, left overnight, the solid filtered off, and dried. The light tan coloured product (1062 g., 80% yield) melted at 61°-63°.

Anal. Calc. for C₁₆ H₁₄ OS: C, 75.57; H, 5.55. Found: C, 75.58; H, 5.74.

EXAMPLE 2 Preparation of 2,3-Dihydro-2-methyl-5,6-diphenyl-1,4-oxathiin from 2-Chloro-2-phenylacetophenone and 1-Mercapto-2-propanol. (Method B)

A mixture of 1-mercapto-2-propanol (19.2 g.) and triethylamine (10.1 g.) in benzene (25 ml.) was added dropwise to a stirred, cooled (20°), solution of 2-chloro-2-phenylacetophenone (23.0 g.) in benzene (200 ml.). The reaction mixture was left at room temperature overnight, washed with water (200 ml.), then with aqueous 5% hydrochloric acid (100 ml.). p-Toluenesulfonic acid (1.0 g.) was added to the benzene solution and the reaction was refluxed for 3 hours with azeotropic water removal. After cooling, the benzene solution was successively washed with 1.0 N sodium hydroxide solution (100 ml.), water (100 ml.) and the benzene removed under reduced pressure. The residue was crystallized from absolute ethanol to give light tan-colored crystals (16 g., 60% yield) melting at 68°-69°.

Anal. Calc. for C₁₇ H₁₆ OS: C, 76.10; H, 6.01. Found: C, 76.14, H, 6.05.

EXAMPLE 3 Preparation of 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin 4-oxide from 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin and 30% Hydrogen Peroxide. (Method C)

To a stirred suspension of 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (63.5 g., 0.25 mole) in glacial acetic acid (200 ml.) was added dropwise 30% hydrogen peroxide (30 ml., 0.26 mole). During the addition the temperature of the reaction mixture was maintained below 25° by cooling in an ice bath. After standing for 12 hours at room temperature, the reaction mixture was filtered and the filtrate was poured, with stirring, into water (1,400 ml.). The crystalline precipitate was filtered, washed with water, and recrystallized from methanol to give colorless crystals (59.6 g., 88% yield) melting at 157°-159° with decomposition.

Anal. Calc. for C₁₆ H₁₄ O₂ S: C, 71.10; H, 5.22. Found: C, 71.22; H, 5.11.

EXAMPLE 4 Preparation of 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin 4,4-dioxide from 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin and 30% Hydrogen Peroxide. (Method D)

To a stirred mixture of 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (12.7 g., 0.05 mole), toluene (25 ml.) and formic acid (4 ml.) was added dropwise 30% hydrogen peroxide (12.5 ml., 0.1 mole). The mixture was refluxed on a steam bath for two hours, cooled, and the solid product was filtered off. The product was recrystallized from absolute ethanol to give colorless crystals (12.5 g., 87%) melting at 178°-179°.

Anal. Calc. for C₁₆ H₁₄ O₃ S: C, 67.12; H, 4.93. Found: C, 66.91; H, 4.93.

EXAMPLES 5-51

Using the procedures of the previous examples and appropriate starting materials, the substituted 1,4-oxathiins shown in TABLE I are prepared. TABLE I gives the systematic name for each product and identifies the method used, and also gives melting point data. In subsequent examples the compounds are identified by the example numbers given in TABLE I.

                                      TABLE I                                      __________________________________________________________________________     SUBSTITUTED 1,4-OXATHIINS                                                      Ex.                               M.P.                                         No.                                                                               Chemical Name         Method   (°C)                                  __________________________________________________________________________     1  2,3-dihydro-5,6-diphenyl-                                                                            A        61-                                              1,4-oxathiin                  63                                           2  2,3-dihydro-2-methyl-5,6-                                                                            B        68-                                              diphenyl-1,4-oxathiin         69                                           3  2,3-dihydro-5,6-diphenyl-                                                                            C        157-                                             1,4-oxathiin 4-oxide          159                                          4  2,3-dihydro-5,6-diphenyl-                                                                            D        178-                                             1,4-oxathiin 4,4-dioxide      179                                          5  2,3-dihydro-6-(4-methylphenyl)-                                                                      B        86-                                              5-phenyl-1,4-oxathiin         87                                           6  2,3-dihydro-6-(4-methylphenyl)-                                                                      C        155                                              5-phenyl-1,4-oxathiin 4-oxide                                              7  2-(4-chlorophenyl)-5,6-dihydro-                                                                      A        92-                                              3-phenyl-1,4-oxathiin         94                                           8  2-(4-chlorophenyl)-5,6-dihydro-                                                                      C        174-                                             3-phenyl-1,4-oxathiin 4-oxide 175                                          9  3-(4-chlorophenyl)-5,6-dihydro-                                                                      A        68-                                              2-phenyl-1,4-oxathiin         70                                           10 3-(4-chlorophenyl)-5,6-dihydro-                                                                      C        108.5-                                           2-phenyl-1,4-oxathiin 4-oxide 110                                                                            ˜140 dec.                              11 3-(4-chlorophenyl)-5,6-dihydro-                                                                      D        152-                                             2-phenyl-1,4-oxathiin 4,4-dioxide                                                                            157                                          12 2-(4-fluorophenyl)-5,6-dihydro-                                                                      A        80-                                              3-phenyl-1,4-oxathiin         82                                           13 2-(4-fluorophenyl)-5,6-dihydro-                                                                      C        153-                                             3-phenyl-1,4-oxathiin 4-oxide 154                                          14 2-(4-fluorophenyl)-5,6-dihydro-                                                                      D        150-                                             3-phenyl-1,4-oxathiin 4,4-dioxide                                                                            152                                          15 3-(3-chlorophenyl)-5,6-dihydro-                                                                      A        65.5-                                            2-phenyl-1,4-oxathiin         67.5                                         16 3-(3-chlorophenyl)-5,6-dihydro-                                                                      C        130-                                             2-phenyl-1,4-oxathiin 4-oxide 131                                          17 3-(4-bromophenyl)-5,6-dihydro-                                                                       A        oil                                              2-phenyl-1,4-oxathiin                                                      18 3-(4-bromophenyl)5,6-dihydro-                                                                        C        135-                                             2-phenyl-1,4-oxathiin 4-oxide 136                                          19 2,3-dihydro-2-methyl-5,6-diphenyl-                                                                   C        145-                                             1,4-oxathiin 4-oxide          147                                          20 2,3-dihydro-5-(4-methylphenyl)-                                                                      A        75-                                              6-phenyl-1,4-oxathiin         77                                           21 2,3-dihydro-5-(4-methylphenyl)-                                                                      C        145-                                             6-phenyl-1,4-oxathiin 4-oxide 147                                          22 2,3-dihydro-5-(4-methylphenyl)-                                                                      D        172-                                             6-phenyl-1,4-oxathiin 4,4-dioxide                                                                            173                                          23 3-(4-fluorophenyl)-5,6-dihydro-                                                                      A        83-                                              2-phenyl-1,4-oxathiin         85                                           24 3-(4-fluorophenyl)-5,6-dihydro-                                                                      C        168                                              2-phenyl-1,4-oxathiin 4-oxide                                              25 3-(4-fluorophenyl)-5,6-dihydro-                                                                      D        152-                                             2-phenyl-1,4-oxathiin 4,4-dioxide                                                                            153                                          26 5-(4-aminophenyl)-2-ethyl-2,3-                                                                       hydrogenation of                                                                        122-                                             dihydro-6-phenyl-1,4-oxathiin                                                                       corresponding                                                                           124                                                                   nitro compound                                        27 2,3-dihydro-5-(2-methylphenyl)-                                                                      A        oil                                              6-phenyl-1,4-oxathiin                                                      28 2,3-dihydro-5-(2-methylphenyl)-                                                                      C        128-                                             6-phenyl-1,4-oxathiin 4-oxide 130                                          29 2,3-dihydro-5-(3-methylphenyl)-                                                                      A        58-                                              6-phenyl-1,4-oxathiin         60                                           30 2,3-dihydro-5-(3-methylphenyl)-                                                                      C        113.5-                                           6-phenyl-1,4-oxathiin 4-oxide 115                                          31 2,3-dihydro-6-[4-(methylthio)phenyl]-                                                                A        130-                                             5-phenyl-1,4-oxathiin         131                                                                            135 dec                                      32 3-(2-chlorophenyl)-5,6-dihydro-                                                                      A        59-                                              2-phenyl-1,4-oxathiin         61                                           33 3-(2-chlorophenyl)-5,6-dihydro-                                                                      C        141-                                             2-phenyl-1,4-oxathiin 4-oxide 142                                          34 3-(4-aminophenyl)-5,6-dihydro-                                                                       hydrogenation of                                                                        96-                                              2-phenyl-1,4-oxathiin                                                                               corresponding                                                                           97                                                                    nitro compound                                        35 3-(4-ethylphenyl)-5,6-dihydro-                                                                       A        oil                                              2-phenyl-1,4-oxathiin                                                      36 3-(4-ethylphenyl)-5,6-dihydro-                                                                       C        oil                                              2-phenyl-1,4-oxathiin 4-oxide                                              37 2,3-dihydro-5-(4-methoxyphenyl)-                                                                     A        oil                                              2-phenyl-1,4-oxathiin                                                      38 2,3-dihydro-5-(4-methoxyphenyl)-                                                                     C        134-                                             6-phenyl-1,4-oxathiin 4-oxide 136                                          39 2-[4-(acetyloxy)phenyl]-5,6-dihydro-                                                                 A        108-                                             3-phenyl-1,4-oxathiin         109                                          40 2-(4-fluorophenyl)-5,6-dihydro-                                                                      A        70-                                              3-(4-methylphenyl)-1,4-oxathiin                                                                              72                                           41 3-(3,4-dimethylphenyl)-5,6-dihydro-                                                                  A        72-                                              2-phenyl-1,4-oxathiin         73                                           42 3-(3,5-dimethylphenyl)-5,6-dihydro-                                                                  A        76-                                              2-phenyl-1,4-oxathiin         77                                           43 3-(3,5-dimethylphenyl)-5,6-dihydro-                                                                  C        143-                                             2-phenyl-1,4-oxathiin 4-oxide 145                                          44 2,3-dihydro-5-(3-methoxyphenyl)-                                                                     A        73-                                              6-phenyl-1,4-oxathiin         76                                           45 2-(2-chlorophenyl)-5,6-dihydro-                                                                      A        71-                                              3-phenyl-1,4-oxathiin         73                                           46 2-(3-chlorophenyl)-5,6-dihydro-                                                                      A        49-                                              3-phenyl-1,4-oxathiin         50                                           47 5,6-dihydro-2-(3-methylphenyl)-                                                                      A        oil                                              3-phenyl-1,4-oxathiin                                                      48 5,6-dihydro-2-(2-methylphenyl)-                                                                      A        57-                                              3-phenyl-1,4-oxathiin         58                                           49 2,3-dihydro-2-methyl-5-(4-methylphenyl)-                                                             A        oil                                              6-phenyl-1,4-oxathiin                                                      50 2,3-dihydro-2-methyl-5-(4-methylphenyl)-                                                             C        150-                                             6-phenyl-1,4-oxathiin 4-oxide 151                                          51 3-(4-chloro-3-methylphenyl)-5,6-dihydro-                                                             A        oil                                              2-phenyl-1,4-oxathiin                                                      __________________________________________________________________________

EXAMPLE 52

To illustrate effectiveness of the described oxathiins as preemergent herbicides, 600 mg chemical is dissolved in 10 ml organic solvent (e.g., acetone) to which 30 mg conventional emulsifying agent (e.g., isooctylpolyethoxyethanol, "Triton X 100" trademark) is added. The solution is diluted to 100 ml with distilled water. Twenty ml of this 6000 ppm solution is diluted to 250 ppm with distilled water. The chemical is applied at the rate of 10 lbs/A (pounds per acre) by drenching 46 ml of the 250 ppm solution on the surface of soil in 41/2 inch plastic pots which had been planted with the following weeds: rough pigweed (Amaranthus retroflexus L.), purslane (Portulaca oleracea L.), tall morningglory (Ipomea purpurea L. Roth), crabgrass (Digitaria ischaemum (Schreb.) Muhl.), Barnyardgrass (Echinochloa crusgalli (L) Beauv.) and giant foxtail (Setaria faberi Herrm.). The percent control of the weeds compared to untreated checks is determined 2 weeks after treatment. TABLE II shows the results with the preemergence herbicides of the invention prepared in accordance with the above examples.

                  TABLE II                                                         ______________________________________                                         Preemergence Herbicides                                                        Percent Control of Weeds Including -                                                 Pig-    Purs-   Tall M. Bnyd- Crab- Giant                                Ex.   weed    lane    glory   grass grass Foxtail                              ______________________________________                                         1     100     100     0       100   0     0                                    3     0       0       0       100   100   100                                  20    0       0       75      90    100   95                                   21    88      100     100     100   100   100                                  22    0       0       0       15    90    75                                   28    0       --      0       50    95    0                                    29    0       0       0       50    95    95                                   30    --      --      0       95    100   100                                  38    0       0       0       95    98    100                                  9     0       0       0       0     50    50                                   10    75      50      40      95    100   100                                  15    0       0       0       50    90    10                                   16    10      0       0       95    100   95                                   17    0       0       0       50    90    10                                   18    90      90      0       90    100   98                                   12    0       0       0       50    95    25                                   13    98      100     0       100   100   100                                  23    0       0       0       0     98    100                                  24    0       90      0       100   100   100                                  25    0       0       0       25    95    100                                  40    0       0       0       75    90    100                                  43    0       80      0       98    100   100                                  2     0       100     0       75    95    90                                   19    100     100     0       95    98    95                                   ______________________________________                                    

EXAMPLE 53

Selectivity of a herbicide is desirable since it allows control of weeds growing among desirable crop plants. To illustrate the usefulness of the oxathiins of the invention as selective preemergence herbicides, 15 mg chemical is dissolved in 5 ml organic solvent containing 25 mg conventional emulsifying agent (e.g., isooctylpolyethoxyethanol) and this solution diluted to 300 ml with distilled water. The chemical is applied at the rate of 2 lbs/A by drenching the surface of soil containing weed and crop seeds in 6-inch plastic pots with 80 ml of the 50 ppm solution. The percent weed control and crop injury are evaluated two weeks after emergence of the crops. TABLE III illustrates the usefulness of these chemicals as selective preemergence herbicides.

                  TABLE III                                                        ______________________________________                                         Selective Preemergence Herbicide Test                                          Percent Weed Control                                                           Wild Texas            % Crop Injury                                                 Wild   Mus-   Pani-                                                                               Quack Bynd  Sugar-     Soy-                            Ex.  Oats   tard   cum  grass grass beets Corn beans                           ______________________________________                                         3    80     70     100  100    100  0     10    0                              21   80     85     100  100   100   0      0   20                              ______________________________________                                    

EXAMPLE 54

Listed below are non-limiting examples of formulations which can be prepared with chemicals of this invention.

    __________________________________________________________________________       10.2% active one lb/gallon emulsifiable concentrate                            a. 2,3-Dihydro-5,6-diphenyl-1,4-oxathiin                                       4-oxide                     61.2 g.                                            b. Chloroform               305.4 g.                                           c. *Triton X-114 (trademark; octyl phenoxy                                     poly ethoxy ethanol)        112.2 g.                                           d. Toluene                  121.2 g.                                            *other surfactants such as Rohm & Haas's                                       AH861 (trademark), anionic/nonionic blended                                    surfactant, can be substituted                                                50% active wettable powder                                                     a. 2,3-Dihydro-6-phenyl-5-(4-methylphenyl)-                                    1,4-oxathiin 4-oxide        40.0 g.                                            b. Emcol L-72-34 (trademark) sodium dodecyl                                    benzene sulfonate           0.8 g.                                             c. Polyfon F (trademark) sodium lignin                                         sulfonate                   0.96 g.                                            d. Dixie Clay (trademark) Kaolinite clay                                                                   9.6 g.                                             e. Hi Sil (trademark) hydrated amorphous                                       silicates                   28.64 g.                                           47.3% active 4 lb/gallon emulsifiable concentrate                              a. 5,6-Dihydro-2,3-diphenyl-1,4-oxathiin                                                                   24.00 g.                                           b. **Triton X-114           5.00 g.                                            c. Naphtha                  21.79 g.                                            **other surfactants such as Rohm & Haas's                                      AH861 (trademark) anionic/nonionic blended                                     surfactant can be substituted.                                              __________________________________________________________________________

EXAMPLE 55

Four crop species are planted in regular potting medium contained in 12 oz styrofoam cups. The four crops are Pinto Beans -- Phaseolus vulgaris; Cotton -- Gossypium hirsutum; Soybeans -- Glycine max and Wheat -- Triticum aestivum L. Six hundred mg chemical is dissolved in 10 ml acetone, 1-3 ml toluene and 30 mg of isooctylphenylpolyethoxyethanol (Triton X100; trademark). This mixture is diluted to a volume of 100 ml with distilled water. This mixture contains 6000 ppm active ingredient by weight. The mixture is sprayed to runoff on the four species aforementioned. The plants are sprayed with a DeVilbiss atomizing sprayer at the following stages of growth.

    ______________________________________                                         Pinto Beans  very early first trifoliate                                       Cotton       fully expanded primary leaf stage                                 Soybeans     first trifoliate nearly expanded                                  Wheat        2-4 leaf stage                                                    ______________________________________                                    

Plant growth regulant observations were made from 5 days after spraying throughout the next 3 weeks. These observations included retardation, formative effects and phytotoxicity. These data are presented in TABLE IV, wherein "retd" stands for retardation, "phyto" stands for phytotoxicity, "N.G." stands for new growth, "trif" stands for trifoliate, and "n.e." stands for no effect.

                                      TABLE IV                                     __________________________________________________________________________     Plant Growth Regulation                                                        Ex.                                                                               Bean     Cotton   Soybean  Wheat                                            __________________________________________________________________________     1  90% retd 30% retd 20% retd 20% phyto                                        3  n.e.     10% phyto                                                                               35% phyto                                                 5  n.e.     10% phyto                                                                               10% phyto                                                                               50% phyto                                        6  n.e.     N.G. sl. slight   10% phyto                                                    deformed                                                                       and      puckering                                                             chlorotic                                                          20 20% retd 80%      80% N.G. 20% retd                                                     terminal retd                                                                  growth                                                                         retarded                                                           21 n.e.     Trifoliates                                                                             N.G.     30% retd                                                     severely retd                                                                           severely darker                                                                epinastic                                                                               green                                            22 n.e.     n.e.     30% retd 5% phyto                                         27 Trifoliate                                                                              25% phyto                                                                               75% phyto                                                                               50% phtyo                                           retd                                                                        28 n.e.     20% phyto                                                                               30% retd n.e.                                             29 Trifoliate                                                                              N.G. 60% 60% retd 10% phyto                                           50% retd retd                                                               30 20% retd N.G. 60% 60% retd n.e.                                                         retd                                                               35 N.G. 50% retd                                                                           N.G. 60% retd                                                                           50% retd n.e.                                                                  dark green                                                36 Trif 75% retd                                                                           N.G. 60% retd                                                                           85% phyto                                                                               --                                               37 N.G. 50% retd                                                                           N.G. 80% retd                                                                           20% retd --                                               38 60% retd N.G. 20% retd                                                                           30% retd 60% retd                                            dark green                 dark green                                       7  75%      N.G. 30% retd                                                                           sl       20% phyto                                           retd     forced terminal                                                                         epinasty                                                              growth                                                             8  n.e.     sl epinasty                                                                             N.G.     10% phyto                                                             epinasty                                                  9  Trif 100%                                                                               100% retd                                                                               80% retd n.e.                                                retd                                                                        10 n.e.     Trif retd                                                                               80% retd 80% retd                                         32 Trif 80% sl epinasty                                                                             30% retd 5% phyto                                            retd              dark green                                                33 n.e.     5% phyto N.G. 60% n.e.                                                                  retd                                                                           dark green                                                15 10% phyto                                                                               terminal 30% retd 10% phyto                                                    80% retd 100% phyto                                                16 20% retd Terminal 80%                                                                            N.G. 100% retd                                                                          20% retd                                                     retd                                                               17 n.e.     80% retd term                                                                           100% retd                                                                               20% retd                                                     stopped                                                            18 30% retd Terminal 80%                                                                            80% retd 30% retd                                                     retd                                                               12 10% phyto                                                                               N.G. 60% retd                                                                           N.G. 100% retd                                                                          15% phyto                                        13 n.e.     N.G. 30% retd                                                                           60% retd 30% retd                                                              dark green                                                                              dark green                                       23 n.e.     20% phyto                                                                               Terminals                                                                               20% retd                                                              60% retd                                                  24 n.e.     Terminal 30%                                                                            60% retd 20% retd                                                     retd                                                               25 n.e.     n.e.     30% retd &                                                                              n.e.                                                                  dark green                                                40 n.e.     N.G. 50% retd                                                                           N.G. 80% retd                                                                           30% retd                                                                       dark green                                       41 n.e.     50% retd 20% phyto                                                                               15% phyto                                        43 n.e.     N.G. 30% retd                                                                           n.e.     n.e.                                             2  n.e.     n.e.     80% retd 10% retd                                         19 60% retd N.G. 30% retd                                                                           60% retd 60% retd                                         45 75% retd N.G. mod 60% retd n.e.                                                         puckered                                                           46 N.G. 35% N.G. 95% 80% retd n.e.                                                retd     killed                                                             47 N.G. dark                                                                               N.G. 95% 40% retd n.e.                                                green    killed                                                             48 N.G. dark                                                                               N.G. 90% 40% retd n.e.                                                green    killed                                                             51 N.G. 80% 30% retd 50% retd n.e.                                                retd                                                                        __________________________________________________________________________

EXAMPLE 56

To further illustrate the utility of these chemicals, data are presented in this Example on the growth retarding properties of soybeans (Corsoy variety). Seventy-five mg chemical is dissolved in 10 ml acetone, 2 ml toluene and 30 mg of Triton X100 (isooctyl phenyl poly ethoxyethanol). This mixture is diluted to a 50 ml volume with distilled water. This mixture is equivalent to 1500 ppm. In some cases a lower rate of 750-800 ppm is used, thus only 38-40 mg are used respectively for the mixture. This mixture is sprayed to runoff on three pots each containing two soybean plants in the early first trifoliate leaf stage. The spray is applied with a DeVilbiss atomizing sprayer. The first height measurement is taken at spraying time and the second when the control plants began to pod or approximately 4 weeks after spraying. A percent growth figure is obtained by using the following formula ##EQU2## where G.C. stands for growth of control plants in cm, and G.T. stands for growth of treated plants. TABLE V shows the unique growth retarding properties of the chemicals on soybeans.

                  TABLE V                                                          ______________________________________                                         Soybean Retardation                                                            Ex.         Rate PPM     % Retardation                                         ______________________________________                                          1           750         76                                                    20           750         90                                                    21           750         67                                                     6           750         57                                                     9          1500         36                                                    10          1500         37                                                    17          1500         30                                                    18          1500         39                                                    28           800         52                                                    29           800         58                                                    30           800         82                                                    37          1500         13                                                    38          1500         76                                                    ______________________________________                                    

EXAMPLE 57

The unique property of these chemicals to inhibit axillary growth is exhibited in this Example. Four hundred mg chemical is dissolved in 10 ml solvent (e.g. toluene, acetone, or mixture thereof) containing 3% surfactant (e.g., isooctylphenylpolyethoxyethanol [Triton X100; trademark], polyoxyethylene sorbitan monolaurate [Tween 20; trademark] or AH831 [trademark] blend of anionic and nonionic surfactants). This mixture, diluted to 100 ml with distilled water, is equivalent to 4000 ppm chemical. Lower dosages may be made by diluting the 4000 ppm formulation or by dissolving less chemical in the solvent mixture. Twenty ml of one of the mixtures described above is sprayed on tobacco plants (Nicotiana tabacum Xanthii variety) at the early flowering stage, but with flowers removed to force axillary growth. The spray is directed to the terminal growing areas in order to facilitate wetting each node as the mixture runs down the central stalk. Percent sucker control data are calculated on the green weight of the suckers which are plucked approximately 4 weeks after spray application. The following formula is used to calculate percent sucker control: ##EQU3## where S.W.C. stands for sucker weight in grams for the control and S.W.T. stands for sucker weight in grams for the treated plant. TABLE VI shows the unique ability of the chemicals to inhibit sucker or axillary bud growth.

                  TABLE VI                                                         ______________________________________                                         SUCKER CONTROL                                                                 Ex.           Rate PPM    % Axillary Bud                                                                 Control                                              ______________________________________                                          1            4000        99                                                    3            1000        88                                                    9            4000        91                                                   10            4000        68                                                   12            4000        100                                                  13            4000        80                                                   20            3000        99                                                   21            3000        99                                                    6            3000        63                                                   30            4000        77                                                   15            3000        76                                                   16            3000        99                                                   17            3000        95                                                   18            3000        91                                                   ______________________________________                                    

EXAMPLE 58

To explain more clearly the activity of this invention on flowering, the following test on chrysanthemum is described. A sprayable formulation is made by emulsifying 1.06 g of a 4 lb active gallon (see Example 54 formulation 3 for composition) containing 2,3-dihydro-5,6-diphenyl-1,4-oxathiin and diluting this mixture to 100 ml volume with water. This mixture is equivalent to 5000 ppm. A respective dosage of 2500 is made by diluting the 5000 ml emulsion. This sprayable formulation is applied to Fred Shoesmith mums that had been exposed to 16 and 23 Short Days (10 hours) to induce flowering. The spray is applied to runoff with a DeVilbiss atomizing sprayer. The plants are placed back in the growth chamber until the total short day period of 6 weeks is completed. They are then removed and placed in a greenhouse until flowering. Data are taken by counting the number of axillary flower buds 1/2 inch or longer below the terminal flower. These data are presented in TABLE VII. The date in TABLE VII illustrate the unique properties of this invention in reducing the number of flower buds that would ordinarily require hand removal.

                  TABLE VII                                                        ______________________________________                                         Chrysanthemum Flowering                                                                                         Average                                                                        Axillary                                                   Rate     Spray      Flower Buds                                   Treatment    PPM      Timing     Per Plant                                     ______________________________________                                         Ex. I Chem.  5000     16 days    4.5                                                                 after                                                                 2500     first 10-  5.3                                                                 hour day                                                              5000     23 days    4.0                                                                 after                                                                 2500     first 10-  5.9                                                                 hour day                                                 Checks                           12.0                                          ______________________________________                                    

EXAMPLE 59

To illustrate further the growth regulating properties of the chemicals on the metabolic activity of plants, 45.6 cc of chemical (formulated as a four pound active gallon -- see Example 54 formulation 3 for composition) were brought up to an 1,892 ml volume with water. This solution was applied at a 3 lb per acre rate in 30 gallons of water to sugarbeets, Beta vulgaris, three weeks before harvest.

The yield data were determined by hand harvesting each of three treatment replicates which consisted of one row 15 feet long. The sugar content was determined by measuring the sucrose content of beets that were randomly selected from each plot.

The data are given in TABLE VIII illustrating the increase in sugar content due to the chemical application. Based on an average yield of 40,000 pounds of beets per acre, the one percent increase would add 400 pounds of extra sugar per acre.

                  TABLE VIII                                                       ______________________________________                                         SUGAR INCREASE                                                                               Rate          Sugar                                              Treatment     (lbs/A)       (%)                                                ______________________________________                                         Ex 1 Chem.    3             16.08                                              "             11/2          15.62                                              Check                       15.05                                              ______________________________________                                    

EXAMPLE 60

To illustrate further the unique growth regulating properties of the chemicals on flowering, 8.5 g. of the chemical of EXAMPLE 1 (formulated as a four pound active gallon -- see EXAMPLE 54 for composition) was brought up to a 400 ml volume with water. This emulsion was applied to four replicate branches of Red Haven peaches that were in the second year of bearing. The flower buds at this time were in the tight bud stage. The chemical emulsion was applied to the branches to the point of run off, with a 1/2 inch brush. The buds were counted and recorded for each branch. Each branch had an average of 35 flower buds. The number of flower buds open were counted 28 and 33 days after application and compared to the original bud count. The percent flowers open figure was established from these two counts, with the results shown in TABLE IX.

A peach farmer is often faced with yield losses due to late frost. The chemicals herein described inhibit flower opening and hence flower kill.

                  TABLE IX                                                         ______________________________________                                         INHIBITION OF FLOWER OPENING                                                   ______________________________________                                                          Percent Flowers Open                                                                 28 days    33 days                                                             after      after                                        Chemical  Rate PPM     Application                                                                               Application                                  ______________________________________                                         Ex. 1     10,000       10.2       17.6                                                    5,000       64.3       91.6                                                    2,500       62.5       100.0                                        Check                  80.0       100.0                                        ______________________________________                                     

We claim:
 1. A method of retarding the growth of plants comprising applying to a locus at which it is desired to retard the growth of plants, in an amount effective to retard the growth of plants, a substituted 2,3-dihydro-1,4-oxathiin chemical of the formula ##SPC3##wherein the R's are the same or different and are selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, chlorine, bromine, fluorine, amino, lower alkylthio and lower acyloxy and n is zero, 1 or
 2. 2. A method as in claim 1, wherein the R's have the following values:R₁ = h r₂ = h, ch₃ or C₂ H₅ R₃ = h, cl or CH₃ R₄ = h, cl or CH₃ R₅ = h, cl, F, CH₃, ##EQU4## or SCH₃ R₆ = H, Cl or CH₃ R₇ = h, cl, CH₃ or OCH₃ R₈ = h, cl, Br, F, CH₃, C₂ H₅, OCH₃ or NH₂ R₉ = h or CH₃ R₁₀ = h.
 3. a method as in claim 2 in which the said chemical is applied in admixture with a surface active agent.
 4. A method as in claim 1 in which the said chemical is 2,3-dihydro-5,6-diphenyl-1,4-oxathiin, 2,3-dihydro-5-(4-methylphenyl)-6-phenyl-1,4-oxathiin, 2,3-dihydro-5-(3-methylphenyl)-6-phenyl-1,4-oxathiin, 2,3-dihydro-5-(3-methylphenyl)-6-phenyl-1,4-oxathiin 4-oxide, 2,3-dihydro-5-(4-methoxyphenyl)-6-phenyl-1,4-oxathiin 4-oxide, 3-(4-chlorophenyl)-5,6-dihydro-2-phenyl-1,4-oxathiin.
 5. A method as in claim 4 in which the said chemical is 2,3-dihydro-5,6-diphenyl-1,4-oxathiin.
 6. A method as in claim 4 in which the said chemical is 2,3-dihydro-5-(4-methylphenyl)-6-phenyl-1,4-oxathiin. 